Twin Falls Power Plant Tour

17 January 2015

Jeff Speer had offered a tour of the South Fork of the Snoqualmie power plant that he manages. Sunday was a perfect day - rainy and windy - and a dozen folks turned out for a pre-tour breakfast at the North Bend Bar and Grill. Ernie was there along with Chris and Patricia, and C.J.B, also Frank with his wife and two young daughters (plus Jeff and two other folks I didn't know). We caravanned to Exit 38 and turned left under I-90. It was a little over a mile to the dam and powerhouse tunnel entrance through a locked fence and gate.

The dam was fully raised since the water flow was low after the recent high water. [When the water level rises, the dam is tilted outward (lowered) using hydraulic power (with cooking oil as the hydraulic fluid).]

 Next we gathered at the tunnel entrance while Jeff raised the gate.

He explained that it was a half-mile hike down a 18:1 slope on a rough road with some running water. No one backed out even with the daunting prospect of the return climb. The roof and sides of the tunnel had been sprayed with "shock-crete" to keep rockfall to a minimum but that didn't do much to keep the water out. There were lots of drips and many starter-stalactites forming "soda straws". About halfway down we stopped for a minute to shut off all lights and experience the effect of full dark (the tunnel made at least two ninety-degree turns). As we approached the bottom we could see the lights from the powerhouse which is about 400 feet below the surface of the water behind the dam. 

Turbine

Only one of the two 13.5 megawatt turbines was running so it was not as noisy as it might have been. We could see that the valve for the intake on one turbine was closed (gravity close, hydraulic open). The intake pipe entered the turbine from below and exited into a larger outflow above the horizontal axle, then the water continued down the tailrace to surface in the river below Twin Falls in the State Park. The generator was spun directly by the turbine axle - no gears. The power house was well-lighted and much drier than the tunnel, warmer too, probably due to the huge spinning chunks of steel. After looking at all the tools (including LARGE wrenches) and bins of fasteners and checking out the powerhouse office, we headed back up. It was a grind for C.J. and me with everyone passing us and waiting for us at the top. It was still drizzling as we broke up and headed back to our cars and the freeway. C.J. invited as many of our paragliding friends as would fit in our living room over for hot spiced cider and cookies. When we realized how late it was (around 1400) we also put out crackers, cheese and chips and hummus. We all had a visit and caught up on C.J.B.'s time in Mexico and other stuff.